A bearing for a fractional-horsepower PMDC electric motor conventionally comprises a first part having axially spaced first and second ends and providing a journal-bearing surface, a second part having radially inner and outer first and second ends which is connected to the first part and provides radial support for the first part, and a third part for engagement with a bearing support. Thus, for a self-aligning bearing having a cylindrical journal-bearing surface and a part-spherical outer surface engageable with the bearing support, the first, second and third parts constitute radially inner, intermediate and outer parts of a ring member and, to provide lubrication, the ring member is normally formed from sintered material which is sufficiently porous to hold, typically, up to 20% of its volume of lubricating oil.
Bearings of this construction function quite satisfactorily, but the cost of manufacture is significant, particularly where the outer surfaces of the bearings have to be part-spherical for self-aligning purposes. Moreover, in some applications, for example: car door locking motors, where the motor is only required to operate intermittently for a small number of revolutions the major problem is reducing static friction, or "stiction". There is insufficient time to develop a friction-reducing oil film and so the cost of providing a lubrication bearing is wasted. In fact, the presence of oil which does little to reduce friction can cause damage by flowing onto the contact surfaces of the commutator because, as a result of the limited operation of the motor, there is insufficient heat to burn this oil to thereby prevent the formation of an insulating coating.